Liquid developer for electrophotography



United States Patent 3,503,881 LIQUID DEVELOPER FOR ELECTROPHOTOGRAPHY Isao Shinohara, Eishun Tsuchida, Toshinao Goto, Zenjiro Okuno', Isao Tashiro, Eiichi Kawamura, and Makoto Nakamura, Tokyo, and Kenkichi Muto, Yokohama,

Japan, 'assignors to Kabushiki Kaisha Ricoh, Tokyo,

Japan, a corporation of Japan No Drawing." Filed June 20, 1967, Ser. No. 650,565

Int. Cl. G03g 9/06 U.S. Cl. 252-62.1 I 2 Claims This invention relates to a novel liquid developer to be used for wet development in electrophotography, and further relates to a liquid developer featuring in dispersion a graft-polymer to be used as the particulate developing agent, comprising a pigment and a polarization-control agent having excellent dispersibility in the liquid.

There are two existing methods for development of electrophotography, namely dry method and wet method; the former employs spreading of dry powdered developing agent on the surface of the latent image; the latter employs wet development by the soaking of sensitized material intoa liquid developer, in which a developing agent is dispersed in an appropriate solvent. The liquid developer to be used in the wet development method is made from pigment and polarization-control agent by kneading them together into paste, followed by the dispersion of the mixture in an appropriatesolvent. Up to the present time, many and various developing agents for use of electrophotography have been proposed; however, commonly used was a rosin, an alkyd resin, and asphalt etc. for dispersing the pigment and for use as a polarization control agent, and a paraffinic hydrocarbon for use as the dispersion medium.

With liquid developers commonly used at present, it is diflicult to achieve constant performance as a polarization control agent, because it is derived from naturally occurring materials such as rosin and asphalt. The variations in composition and property of such a natural material would not exist in a manufactured product. In addition, when the developer is used for long term, the dispersibility becomes inferior, and this results in coagulation and precipitation of the particulate developing agent and, therefore causes the development capacity to be lowered, and the image developed to lack sharpness. The deterioration in dispersibility and other defects are believed to result from the fact that the particulate developing agent exists in the liquid in a form to cause the particulate pigment dispersed in the solvent to attract the molecule of polarization control agent in the commencing period of use, so that stabilized dispersion is maintained during this period, but that after repeated use for long term, the dissolved matter separated from the photoconductive layer of the photosenstive material accumulates, or the molecule of polarization control agent gradually escapes from the particulate pigment owing to the charge of liquid.

v The liquid developer of the present invention to be used for electrophotography is a research result achieved after doing wide investigations aimed as improvement in dispersibility and stabilization of particulate developing agent contained in the liquid developer. This does not, at all, use the naturally occurring materials such as rosin and asphalt, and is entirely different from the existing developers, and is an entirely new improved type, having no such defects as mentioned above, and involving the dispersion into the liquid of particulate developing agent obtained by the direct chemical combination of polarization control agent with the pigment. In the liquid developer of the present invention, the monomer of acrylate ester having the following formula is polymerized after kneading with carbon black, initiator of the polymerization reaction, and with benzene, and the particulate developing agent which is formed by the reaction and is in a form having graft-polymerized monomer of acrylate ester onto the particulate carbon, is directly dispersed into parafiinc organic solvent heretofore used for such purposes, to prepare the developer of this invention. In the formula, R is H, CH or C H and 2 is s w C8H1'I: 10 21 12 25: r 14 29 As will be exemplified later for purposes of contrasted comparison in the case of polymerization of carbon black with substances other than acrylate ester as presented by the foregoing general formula, for instance, styrene or butyl acrylate etc., the obtained product was, at all, unusable for the purpose as the liquid devloper.

The liquid developer to be used in this invention is that illustrated in the foregoing, but the mechanism of the graft-polymerization is not yet clarified at present. Anyhow, this graft polymer of carbon-acrylate ester could become sharply charged developing agent particles by itself when dispersed inordinary parafiinic solvent, and the dispersibility in the dispersed liquid is quite excellent and displays stabilized development capability even after long term use of the liquid developer. Accordingly, the liquid developer of the present invention could have constant quality which comes from nature of the synthesized raw materials, and furthermore, this does not require various additives as was used in conventional manufacture. However, to obtain further increased sharpness of the image using this developer, the concurrent use of small amount of higher fatty acid or metallic soap is effective.

This invention can be understood better by the detail EXAMPLE 1 A 10 gram of lauryl acrylate, 10 gram of carbon black (from Mitsubishi Chemical Company, #44), 0.21 gram of azobisisobutylonitrile (being initiator), and 6.5 gram of benzene were mixed and kneaded, then put into polymerization tube followed by freezing, and degasified under reduced pressure, and was sealed. This was then shaken for 8 hours at 60 deg. C. in the polymerization tank of shaking type. Then, 0.5 gram of the reaction product was put into mortar together with 5 gram of toluene, and after well kneading, this was dispersed into 500 cc. of isoparafiinic hydrocarbon solvent (Isopar H), thus obtaining liquid developer for the use. The particulate developing agent of the liquid developer showed stabil- Carbon Azobis Black Benzene isobutyl- (g.) Monomer (g.) (g.) onltrile (g.)

A 1O 10 acrylic acid 23. 2 0. 73

B 10 5 acrylic acid .4- 11. 6 0. 37

C 10 10 butyl acrylate 12. 2 O. 38

D 10 10 styrene 15. 0. 47

EXAMPLE 2 A 0.5 gram of polymerized product obtained in the former example was kneaded together with grams of toluene, and followed by further addition and kneading with 0.5 gram of 1 percent in toluene solution of aluminum monostearate. This was dispersed into into 500 cc. of isoparafiinic hydrocarbon (lsopar H), thus obtaining liquid developer. Photosensitive material of electrophotography having latent image was immersed into the liquid developer, and P/ P type image was obtained which was more sharpened than the former example.

What we claim is:

1. A liquid developer for use in electrophotography comprising a dispersion of particulate developing agent in parafiinic hydrocarbon solvent, said particulate developing agent is composed of reaction product made by graft-polymerization to carbon black with an acrylate ester indicated by the following formula, where;

1 is CH3 0r z s; and R3. i E 13: vC8 11? CIOHZI, 12 25, or 14 29- v 1 CH2=C 2. A liquid developer for use in electrophotography comprising a dispersion of particulate developing agent and a small amount of a metallic soap, into parafiinic hydrocarbon solvent, said particulate developing agent composed of reaction product made by graftpolymerization to carbon black with an acrylate ester indicated by the following formula, where; R1 is H, CH3 01' 021-15; and R2 iS C6H13', I'I 'I, C10H21, C12II25, 01' CMHZQ.

COORQ References Cited UNITED STATES PATENTS 9/1966 Russell 106 3'.s

GEORGE F. LESMES, Primary Examiner J. P. BRAMMER, Assistant Examiner U.S. c1. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 35 3 Dated March 3 97 Isao Shinohara, Eishun Tsuchida, Toshinao Goto,

I sll Makoto Nakamura, and Kenkichi Muto It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Inventor(s) Column 4, line 14, after-"CH insert line 14, the formula reading "C H shoul read (3 H SIGNED AND SEALED JUL 2 8 1970 Aunt:

Edwin! n. Fletch I mm m o fi oomiasione'r of Pawn-t! USCOMM-DC COSTS-P69 FORM PO-105O (10-69) u.s oovumnim mnmur. orncc 1 ml o-au-Ju 

